1. Field of the Invention
This invention relates to the means and methods for the slip forming of reinforced composite concrete structures, having functionally discrete components, for road and bridge construction. More specifically, this invention is directed to the use of a series of tunnel molds, including a first tunnel mold for forming monolithic structure, including a moment or junction slab with exposed rebars, for later integration into an additional structure (e.g. coping or traffic railing). In the exemplary embodiments of this invention, the structure formed upon, and integrated with exposed rebar extending from an antecedent component (such as a moment or junction slab), can include any one, or combination of components slip formed components, such as a coping, traffic rail and/or barrier wall (e.g. opaque traffic wall, sound wall or impact resistant wall).
2. Description of the Prior Art
Slip forming of concrete structures is a well-known technique for preparation of structural concrete elements for various industrial and public works (road, conduit, etc.) projects. Slip forming is a construction method in which a quick setting concrete is poured into the mold cavity of a mold, and the mold is progressively advanced or “slipped” over an iron work array composed of rebars, as the mold cavity the progressively advanced and lays down concrete over the iron work array. The rate of advancement of the mold, relative to the iron work array, is determined, in part, by the green strength of quick setting concrete in the formed concrete structure, specifically, the extent to which the concrete in the formed structure is self-supporting, and is capable of supporting a forward advancing mass of unset concrete, as additional concrete leaves the confines of the slip-mold and is deposited on the iron work array by the forward advancing mold.
Slip forming, thus, enables continuous, non-interrupted, cast-in-place “flawless”, (i.e. seamless—no joints), concrete structures, which have superior performance characteristics to piecewise construction, using discretely formed elements. Slip forming relies on the quick-setting properties of concrete, and requires a balance between quick-setting capacity and workability. Concrete needs to be workable enough to be placed into the form and consolidated, (via vibration), yet quick-setting enough to emerge from the form with strength (also “self-supporting strength” or “green strength”). This green strength is needed because the freshly set concrete must not only permit the form to “slip” upwards/forward, but also support the freshly poured concrete above it (“vertical slip forming”) and/or the freshly poured concrete in front of it (“horizontal slip forming”).
In vertical slip forming, the concrete form may be surrounded by a platform on which workers stand, placing steel reinforcing rods into the concrete and ensuring a smooth pour. Together, the concrete form and working platform are raised by means of hydraulic jacks. Generally, the slip-form rises at a rate which permits the concrete to harden (develop green strength) by the time it emerges from the bottom of the form. In horizontal slip forming for pavement and traffic separation walls, concrete is laid down, vibrated, worked, and settled in place, while the form itself slowly moves ahead. This method was initially devised and utilized in Interstate Highway construction initiated by the Eisenhower administration during the 1950s.
The following text provides a representative, (not exhaustive), review of the prior art in this field:
U.S. Pat. No. 3,792,133 (to Goughnour issued Feb. 12, 1974) describes a method and an apparatus for concrete slip forming a highway barrier wall of varying transverse cross-sectional configuration for accommodating different grade levels on opposite sides of the wall, and wherein variations in the wall cross-sectional configuration may be readily accomplished during wall formation without requiring stopping, realignment or other interruptions in the screed movement during wall forming.
U.S. Pat. No. 4,266,917 (to Godbersen issued Mar. 12, 1981) describes a method for the efficient slip forming of highway median barrier walls of differing size (adjustable height) and shape having any arrangement of linear and curved sections and while the machine is being advanced in a single direction. The lateral adjustability of opposite side walls of the form, relative to the top wall, permits the use of the side walls with top walls of varying widths. The relative vertical adjustment of the top wall and side walls provides for a wide variation in the vertical height of a barrier wall particularly where a glare shield is to be formed on the barrier wall top surface. The slip forming of the glare shield takes place simultaneously and continuously with the slip forming of the barrier wall and over any selected portion of the wall while the machine is being advanced in a single direction. At any adjusted position of the slip form, the skirt member associated with each side wall is adjustable to prevent any flow of concrete from between the ground or highway surface and the form.
U.S. Pat. No. 4,084,928 (to Petersik issued Apr. 18, 1978) describes an improved barrier forming apparatus and method whereby a barrier is formed continuously over a surface, the barrier having continuous reinforcing rods extending the length of the barrier and having cage reinforced standard supports at predetermined intervals along the length of the barrier. The Petersik improved barrier forming assembly comprising a concrete forming member having a form cavity extending there through; a concrete passing member having a concrete delivery opening for passing concrete or the like to the form cavity; and a positioning assembly comprising a support shaft and a door member pivotally supported at a forward end of the concrete forming member, the barrier being extrudable continuously via the form cavity from a rearward end of the concrete forming member. The door member selectively is positionable to partially seal the form cavity at the forward end of the concrete forming member and has rod clearance channels through which the reinforcing rods pass through the door member into the form cavity when the door member is so positioned to seal the form cavity. The rod clearance channels permit the door member to pass the reinforcing rods to open the form cavity at the forward end of the concrete forming member to allow the free passage of the barrier forming assembly over the cage reinforced standard supports.
U.S. Pat. No. 5,290,492 (to Belarde, issued May 1, 1994) describes a system for continuously forming a concrete structure (a) having a predetermined cross-sectional configuration, (b) which extends along an elongate path, and (c) includes an outer surface having a textured pattern comprising concave or convex portions which extend other than just parallel to the elongate path. The system includes a frame, a first form assembly, a second form assembly, a drive system, and a support assembly.
Efforts at slip forming highway structures with exposed rebars have been previously attempted, and unsuccessful for a variety of reasons—not the least of which being that the means and methods adopted do not comport with the engineering requirements of established highway structure specifications which have been issued by both state and federal departments of transportation. Such proposed alternatives to established engineering norms are, thus, neither instructive nor suggestive of solutions to the deficiencies/limitation in well-known and established slip forming construction techniques.
On example of such non-conforming means and methods for slip forming sound walls, (having sequentially formed sections or tiers), is disclosed in Korean Patent No. KR 10-1286959 B1 (to Kim, published Jul. 23, 2013). In the Kim publication, he discloses the slip forming of a sound wall, by progressive or sequential slip forming of a series or sections of the sound wall on top of one another. Each of these sequentially formed sections are connected to one another, with a portion a of rebar, which has been excavated and pried from within the consolidated/hardened concrete of a prior formed slip formed sound wall section. More specifically, the means and methods adopted by Kim are unorthodox, weaken the rebar connection between each of the sections of the sound wall because they require (a) initially providing an iron work array, wherein the rebars of the array have been deformed by bending the top portion of each at right angles, to accommodate their passages through a conventional closed cavity slip mold; (b) slip forming a section of sound wall on such deformed iron work array, wherein the entire iron work array is initially embedded in concrete, and (c) chiseling or prying the deformed rebars out of concrete from the top of the slip formed section of the sound wall section, (d) straightening the deformed top portion of rebar, to provide an erect section or portion thereof for splicing with additional similarly deformed rebars, to form a second rebar array (wherein top portion of each spliced rebar is also bent at right angles), and (e) slip forming the a successive section of sound wall onto this similarly deformed second rebar array. This process is sequentially repeated until the Kim sound wall attains it desired design height. The Kim means and methods, as above described, obviously do not conform to established and accepted engineering practice, (e.g. bending and straightening of reinforcing rebars); and, notwithstanding, the ability to create a connection between successively formed sections of slip formed sound wall, the sections of excavated rebar from one antecedent wall section, do not provide an acceptable the means and method for reinforcing of successive slip formed components of a unitary composite.
Up to now, the standard or generally accepted techniques for the fabrication of reinforce concrete structures, such as bridge coping for an overpass on the highway, have required either the use of a pre-cast coping element (fabricated off-site), and/or the manual casting of a coping on-site, utilizing traditional forms and concrete casting techniques. In the case of a pre-cast concrete coping element, the road bed of the overpass requires special preparation since the pre-cast element does not readily conform to the angle of incline or grade of a ramp or overpass and, therefore, imperfectly abut one another upon placement on the incline of the bridge overpass. Accordingly, additional installation expense is required to insure the connection of abutting pre-cast copings to one another to insure the formation of a unitary coherent structure.
Alternatively, the on-site casting of an overpass/bridge coping, using the a manual process for forming the coping, specifically, traditional forms and concrete casting techniques, is preferably to the pre-cast coping, because the resulting coping is structurally continuous, and better conforms to the incline/grade of the ramp or overpass. Notwithstanding, the on-site casting of a bridge coping, by traditional concrete casting techniques, is very labor intensive and does not, without an inordinate amount of man power, lend itself to rapid fabrication and accelerated completion schedules. Current building specifications do not, however, generally permit the use of either technique for the formation of concrete structures having rebars extending from within the formed component because of the inability to integrate the rebars embedded within the concrete structures, with the rebars which extend from the concrete structures.
As is evident from the above, there are number of alternatives for the slip forming of structures for use in road and bridge construction. The numerous alternative systems have their proponents and their detractors. In the context of selection of the more appropriate and efficient system, for example, for construction of various road way structures, such as bridge copings, road bed pads, retainer/barrier walls and/or glare shields, time is money, and often is reflected in the bidding process. More specifically, the bid letting on highway construction projects routinely include both penalty provisions for tardy completion and/or bonus payments for early completion. Accordingly, efficiencies which advance project completion, generally translate into both cost saving and increased profits. Thus, there are continuing efforts to automate, where possible, the method for the fabrication of structural concrete components in highway construction; and, thereby standardize the method for the fabrication of certain roadway construction components. This is particularly appropriate in the case of roadway construction being bid and undertaken on an interstate and/or federally funded highway construction projects.
Slip forming is one such advancement (standard), which been adopted for reducing manual/traditional concrete casting of structural highway components fabrication of a limited number of concrete structures, (e.g. Jersey barrier). This process has, however, remained relatively unchanged for more than 35 years; and, unfortunately has been limited to forming of structures which do not readily lend themselves to further integration with additional, complementary components.